A stacking apparatus including sticker placement mechanism is disclosed in commonly assigned U.S. Pat. No. 6,048,164. The present invention is directed to a sticker transfer arm having particular application to the sticker placement mechanism of that application and the disclosure therein is incorporated herein by reference.
In the above-referenced disclosure, lumber stacking forks oscillate back and forth between a lumber infeed conveyor and a stack of lumber for transferring tiers of lumber from the conveyor to the stack. The forks carry sticker pans and a sticker infeed conveyor brings stickers to a location near the retracted position of the forks and sticker transfer arms are cooperatively cycled to transfer stickers into the path of the forks for loading the stickers into the sticker pan.
There are three apparatus motions that are cooperatively cycled to achieve the above functions. The three apparatus referred to are the forks, the transfer arms and the sticker conveyor. The forks oscillate in a rectangular-like path. Upon receiving the stickers and lumber tier, the forks move along an upper path to a position over the stack. The forks then move downward to deposit the stickers and lumber tier onto the stack. The forks then retract along a lower path to a position ready to receive the stickers and lumber tier. The forks then raise to the position of the upper path and in the process receive the stickers and lumber tier.
The movement of the forks in the oscillating path is substantially continuous and the other two apparatus have to be cycled in time to the proper positions. The transfer arms have an upper position where a sticker is positioned in an extended finger at the distal end of the sticker arms directly in the path of the fork in its upwardly directed movement. The sticker pans on the fork are slotted at positions aligned with the fingers so that the fingers can pass downwardly through the pans and in the process the stickers are transferred to the pan. It is important that the transfer arms have reached this upper position before the forks are fully retracted.
The arms lower the fingers down through the pan slots of the fork and into the path of stickers being conveyed on the infeed conveyor. The stickers are spaced apart on the conveyor and the fingers dip down between the spaced apart stickers. The stickers are moved by the infeed conveyor over the fingers and the fingers are raised to lift the stickers from the conveyor and into the upper position for transfer to the fork. The infeed conveyor has to be accordingly timed with the arm movement to provide a space for the finger to move into the conveyor path and then move stickers into position over the fingers.
It will be appreciated that a number of situations can occur to upset the timing of these movements. If a sticker is mis-located on the sticker conveyor, the transfer arm when lowered into the conveyor path, can engage (crash) that sticker. If a sticker is broken and a portion hangs below the fingers during the transfer mode, the forks and/or pans on the fork when sliding under the fingers can engage (crash) with the broken sticker to apply a sideway directed force on the transfer arms.
Any crash as between the fingers and the fork (e.g., resulting from a broken sticker) or, as between the fingers and the sticker infeed conveyor (e.g., resulting from a mis-located sticker) can result in damage, e.g., to the sticker transfer arms. The stacker has to be shut down and repairs made at a significant cost.